The present invention relates to golf shafts, and more particularly to a golf shaft which can exhibit a vibration characteristic extremely close to the vibration characteristic exhibited by a steel shaft without impairing at all the characteristic of a so-called carbon shaft.
Golf shafts include a steel shaft, a carbon shaft and the like. The carbon shaft has the merit in that the carbon shaft is ligher than the steel shaft, and therefore carbon shafts are being widely habitually used these days. However, the carbon shaft has a problem in that a sense of flexure like a steel shaft cannot be obtained.
This will be explained with reference to FIG. 6 which shows attenuation of a vibration. In FIG. 6, the solid line indicates the case of a carbon shaft whereas the broken line indicates the case of a steel shaft. As will be apparent from FIG. 6, in the case of the steel shaft, since the damping factor is low, it takes some time till the vibration is damped. On the other hand, in the case of the carbon shaft, since the damping factor is high, the vibration is damped early.
The damping characteristic of vibration will be discussed in relation to the swinging operation of golf. A golf swing moves to a back swinging from in address state and thence to a top state. Then, a down swing is effected to hit a ball.
At that time, in the case of the steel shaft, the shaft is rearwardly flexed by the back swing, and the flexed state thereof is maintained in the course of the down swing. This results from the fact that the damping factor of vibration is low, as previously mentioned. The shaft is returned forwardly when it hits a ball, and therefore, a sufficient head speed is obtained.
On the other hand, in the case of the carbon shaft, since the damping factor of vibration is high, as previously mentioned, the flex state cannot be sufficiently maintained in the course of the down swing and the shaft becomes returned. Therefore, the "sense of flexure" is not sufficiently secured and the head speed becomes slow.
A proposal has been made, as shown in FIG. 7, in which metal fiber (for example, amorphous fiber, stainless steel fiber, etc.) 103 is spirally wound about an inner layer or an outer layer of a carbon shaft 101.
However, the aforementioned proposal is made principally to prevent torsion of the shaft but not to improve the flexing characteristics.